This invention relates generally a process of adjusting the water vapor transmission/porosity of films and film composites, while maintaining general resistance to liquid transmission (strikethrough). More specifically this invention is directed towards a process for producing films, film composites, and articles made therefrom, that are made permeable to water vapor, by passing them through interdigitating grooved rollers.
Polyolefin films which are rendered more permeable to water vapor using filler loading and orientation are known.
Such films or film composites are said to be more breathable, that is to have improved, increased permeability to water vapors, while maintaining a resistance to liquid strikethrough (defined herein). Uses of such films or film composites include on a diaper the permeability of which may permit the passage of moisture vapor and air, while substantially preventing the passage of liquid. The advantages of such a film used in a diaper are that after the wearer voids, the liquid is generally retained, while much of the liquid vapor can escape decreasing the xe2x80x9cwet feelingxe2x80x9d, and lowering the possibility of uncomfortable diaper rash.
U.S. Pat. No. 4,472,328, assigned to Mitsubishi Chemical Industries, Ltd., suggests a breathable polyolefin film prepared from a polyolefin/filler composition having from 20 percent to 80 percent by weight of a filler such as a surface treated calcium carbonate. A liquid or waxy hydrocarbon polymer elastomer such as a hydroxyl-terminated liquid polybutadiene was purported to produce a precursor film that could be mono-axially or biaxially stretched to make a film breathable. The breathable film described by Mitsubishi is also described in Great Britain Patent No. 2,115,702, assigned to Kao Corporation. The Kao patent further describes a disposable diaper prepared with a breathable film as disclosed by the Mitsubishi patent. The breathable film is used as a backing for the diaper to contain liquid.
U.S. Pat. No. 4,350,655, assigned to Biax Fiber Film, describes a porous polyolefin film containing at least 50 percent by weight of a coated inorganic filler. The precursor film is formed without the addition of an elastomer by employing an inorganic filler surface coated with a fatty acid ester of only silicon or titanium. The precursor film is then rolled between horizontally grooved rollers. Cold stretching of the precursor film at a temperature below 70xc2x0 C., produces a porous film. Some of the resulting films were stated to be both vapor and liquid permeable, however, at least one film (Example 3) was stated to be permeable to air.
U.S. Pat. No. 4,777,073 suggests a breathable film produced by stretching of a precursor film prepared from a polyolefin/filler composition. The document suggests that the permeability and strength, especially tear strength are improved by melt embossing the precursor film with a patterned melt embossing roller and stretching the film to impart a pattern of different film thickness having greater permeability within the areas of reduced thickness compared to the areas of greater thickness.
Most of these techniques require that a film or film composite be rendered breathable, regardless of the technique but generally through tentering (for transverse direction or TD orientation, and differential speeds of two rolls for machine direction or MD orientation), in a separate operation, prior to final construction of the end-use article, for instance the diaper, leading to expensive double processing or more expensive transport of the film rendered less dense by the tentering operation.
Therefore, a commercial need exists for a process that can be used to improve (increase) the film or film composite water vapor transmission rate (WVTR) at a commercially acceptable rate with existing commercial equipment, such that the disposable article will have relatively high water vapor transmission rates in all or part of the article, with good resistance to liquid permeability, while maintaining a sufficient level of physical strength to form a useful disposable article. A process for attaining such an article at relatively rapid, economical rate would be advantageous.
We have discovered that certain polyolefin films and film composites can be processed to have greater water vapor transmission rates, relatively low liquid strikethrough, while maintaining film integrity, by using certain film forming formulations and techniques and passing the film, the film composite and/or the finished fabricated disposable article, through a nip of at least one pair of interdigitating grooved rollers.
In certain embodiments of our invention a polyolefin film or film composite comprises at least one layer of a disposable article and is rendered breathable by passing the film, film composite or fabricated article through interdigitating grooved rollers. The film, film composite or fabricated article will have either a single layer or multilayer construction and the polyolefin/filler combination can be co-extruded, laminated or blended with other polymers or polymer based fabricated articles.
In an embodiment of our invention, a film (xe2x80x9cprecursor filmxe2x80x9d) is made, utilizing a polyolefin or a polyolefin blend with a relatively higher filler loading, generally including embossing a pattern thereupon, such that its subsequent manipulation, either by itself, in a film composite or as a part of a disposable article, will render the film breathable (hereinafter defined as water vapor permeable, within certain limits of water vapor transmission rates (WVTR), while maintaining a certain level of liquid impermeability) while maintaining a minimum level of physical properties, elongation/tensile strength being of most importance. The manipulation of the film, film composite, and/or fabricated disposable article includes passing all or parts of the film, film composite, and/or fabricated disposable article through a grooved roller and/or interdigitating grooved rollers, at a rate sufficient to develop a minimum level of breathability to the film or film portion of the article, at a commercial and economical rate.
The tear strength, elasticity, and softness of a film prepared from the polyolefin/filler composition may be improved by addition of small amounts of an olefinic elastomer.
The WVTR desired is above 100 g/m2/day@38xc2x0 C., 90% RH preferably above 200 g, and can be easily greater than 1000 g/m2/day.